GB2344041A

GB2344041A - Apparatus for automatically correcting a CRT monitor for earth's magnetic field

Info

Publication number: GB2344041A
Application number: GB9927482A
Authority: GB
Inventors: Kyung Sic Kim; Jin Sik Kim
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 1998-11-19
Filing date: 1999-11-19
Publication date: 2000-05-24
Anticipated expiration: 2019-11-19
Also published as: KR20000033114A; BR9905643A; ID25711A; DE19955497A1; KR100296301B1; TW509883B; GB2344041B; GB9927482D0; CN1105355C; US6501222B1; CN1254880A; DE19955497B4

Abstract

An apparatus for automatically correcting for the earth's magnetic field includes: a peripheral magnetic field sensing unit 210 for sensing a variation in a magnetic field and generating a corresponding frequency; a frequency producing unit 220 for arithmetically operating the frequency generated from the peripheral magnetic field sensing unit and producing frequencies corresponding to each direction; a correction amount computing unit 200 for computing each correction amount corresponding to the frequencies of each direction produced by the frequency producing unit; and a deflection correction unit 240 for correcting a deflection error of the monitor as much as the corrected amount in the correction amount computing unit. By having such construction, a screen is automatically corrected by sensing a peripheral magnetic field with a small memory capacity, thereby attaining users' convenience in correcting an ambient magnetic field and maintaining an optimum picture quality.

Description

2344041 APPARATUS FOR AUTOMATICALLY CORRECTING FOR EART

MAGNETIC FIELD FOR MONITOR

The present invention relates to a correction for earth magnetic field for a monitor of a computer, and more particularly, to an apparatus for automatically correcting for earth magnetic field for a monitor for improved picture quality, including distinct colors and improved screen centering.

In general, a magnetic field in space, represented by a three dimensional vector, can be used for deflection in a monitor of a computer.

Accordingly, if an orientation-of the monitor is changed or the monitor is moved to another area, the peripheral magnetic field is changed, causing a reduction in picture quality from the monitor.

In order to resolve such a problem, such techniques for correcting an earth magnetic field have been proposed, which provides better picture quality of the monitor.

Examples are Korean patent publication No. 96-16849 and Korean Laid Open No. 95-24598.

Referring to Figure I of the drawings, Korean patent publication No. 96 16849 discloses apparatus for correcting an earth magnetic field including: a standby power supply unit I I for outputting a constant voltage Vcc as power is supplied; a remote controller 20 for setting an operation state of a TV system and selecting an earth magnetic field correction mode; a remote- controller receiving unit 19 for receiving a transmission signal of the remote- controller 20; a pre-amplifier 18 for amplifying the output signal from the remote- controller receiving unit 19 to a predetermined level; a microprocessor 15 for decoding the output signal from the pre-amplifier 18 and outputting an on-screen display indicating a compass direction of a corresponding mode for setting a correction 2 mode and a signal for controlling the corresponding mode when the earth magnetic field correction function is selected, upon receipt of the output Vcc from the standby power supply unit 1; a chroma unit 16 for indicating the compass direction according to the setting of the correction mode of the CPT (color picture tube) upon receipt of the output signal from the microprocessor 15; a current switching unit 14 for switching on and switching off a current flow of a device coil 12 according to a relay drive signal S 1 of the microprocessor 15; and an earth magnetic field correction unit 17 for controlling the direction and the strength of the current according to mode signals S3-S5 of the microprocessor 15 to minimize influence of the earth magnetic field. The current switching unit 14 includes a transistor Q I and a relay RY 1.

The earth magnetic field correction unit 17 includes transistors Q7 and

Q8 of which each emitter is grounded through resistances RIO and R13 and each base is connected to output terminals S-3) and S5 of the microprocessor 15 through resistances RI I and R14, a transistor Q2 of which the emitter is grounded and the base is connected to an output terminal S4 of the microprocessor 15 through a resistance R2, transistors Q3, Q4, Q5 and Q6 of which each base is commonly connected to a terminal at one end of each resistance R') and R4 and each emitter is commonly connected and an earth magnetic field correction coil L2 and a condensor C I are respectively connected between the contact points, transistors Q3 and Q5 of which collectors are commonly connected and its contact point is connected to a voltage B+ through a resistance R7 and the collector of the transistor Q7 and a terminal at other end of the resistance R3 are commonlN connected through the resistance R9, and the collector of the trarisistor Q8 is connected to a terminal at the other end of the resistance R4 and its contact point is connected to the voltage B+ through the resistance R12, and transistors Q4 and Q6 of which collectors are 3 commonly connected and its contact point is grounded through a resistance R5, a resistance R6 is connected to the collector of the transistor Q2 through a resistance R6.

The remote-controller 20 includes a compass to identify an orientation of the TV, for the purpose of correcting the earth magnetic field.

The operational process of the apparatus for correcting an earth magnetic field in accordance with the conventional art will now be described with reference to Figures 2 through 4.

First, when the power is ON, the standby power supply unit I I outputs the constant voltage Vcc to the input terminal S2 of the microprocessor 15, and accordingly, the microprocessor 15 in a standby state checks the output signal of the pre-amplifier 18.

At this time, when the power key is in an OFF-state, the microprocessor outputs the relay drive signal S I to the current switching unit 14 to turn off the transistor Q1 to thereby turn off the relay RYI, and also outputs the earth magnetic field correction signals S3-S5 of low voltage to maintain OFF- state of the system.

When a power key is inputted from the remote-controller by the user, the transmission signal of the remote-controller 20 is received by the remote controller receivina unit 19, and the received signal is amplified by the pre amplifier 18 to a predetermined level and then outputted to the microprocessor 15.

Upon receipt of the output signal from the pre-amplifier 18, when the microprocessor 15 discriminates the input of the power supply key by decoding and outputs the relay drive signal. S I to the current switching unit 14, the transistor Q I is turned on to drive the relay RY 1, according to which the contact points 'a' and 'b' are connected and power is supplied to the power supply unit 4 13, so that the device coil 12 controls the current flow.

In other words, when the power is ON, a current flows through a thermistor TM and the coil L I of the drive coil 12, and as time goes by, since the resistance value is increased according to temperature characteristics of the thermistor TM, and thus, little current flows through the coil Ll, the magnetic field of the monitor is degaussed.

Meanwhile, when the power is ON, the microprocessor 15 determines whether or not the earth magnetic field correction key was selected. In this respect, if there is no key selection, it returns to the initial step of the operation.

If the earth magnetic field correction key is selected on the remotecontroller 20 by the user, the microprocessor 15 senses the key input through the remote control receiving unit 19 and the pre-amplifier 18 and performs decoding. The earth magnetic field correction function is actuated by this decoding.

The microprocessor 15 then outputs a compass direction indication signal OSD to the chroma unit 16. Then, an on-screen is generated on a CPT (color picture tube) screen, and the user selects a key on the remote- controller corresponding to the TV orientation by using the compass attached on the remote-controller 20. Thus, a mode corresponding to the orientation of the TV set can be set by shifting the earth magnetic field correction mode step by step.

That is, as the user presses the earth magnetic field correction mode setting key on the remote-controller 20 after ascertaining the orientation of the TV, the microprocessor 15 outputs the on-screen display signal OSD for the corresponding mode to the chroma unit 16, so that the on-screen display according to each mode is sequentially displayed on the screen of the CPT. In this respect, at the time the on-screen display consistent with the orientation of the TV, as identified by the compass attached on the remote-controller 20, is displayed the user selects a set key to set the corresponding mode.

For example, if the TV set is turned 30' (A' direction) from a given orientation, the earth magnetic field setting on the on-screen display is set to the

A' direction after the earth magnetic field correction mode is selected.

When the setting of the earth magnetic field correction mode is completed, the microprocessor 15 outputs the earth magnetic field correction signals S3, S4 and S5, according to the corresponding modes as set, to the earth magnetic field correction unit 17.

In detail, when the orientation of the TV set is identified as a standard direction and 'ModeO' is selected, since the microprocessor 15 outputs only earth magnetic field correction signals S3 and S5 as a high voltage to the earth magnetic field correction unit 17, the transistors Q7 and Q8 are turned on while the transistors Q3 and Q5 are turned off. Then, since the current does not flow through the earth magnetic field correction coil L2, earth magnetic field correction is not performed.

Meanwhile, when the direction of the TV set is identified as 'A' direction and "Model' is selected, since the microprocessor 15 outputs only the earth magnetic field correction signal S3 as a high voltage, the transistors Q4,

Q5 andQ7 of the earth magnetic field correction unit 17 are turned on, so that a little current flows in the 'A' direction (that is. B+ -- R7 -+ Q5 --+ L2 --+ Q4 --+ R5), thereby correcting to the degaussed state.

If the earth magnetic field correction mode is changed to be set by

Mode2' from 'Model', the orientation of the TV set is identified as a 'C' direction, so that the microprocessor 15 outputs the earth magnetic field correction signals S3 and S4 as a high voltage. Then, the transistors Q2, Q4, Q5 and Q7 of the earth magnetic field correction unit 17 are turned on, so that the current flowing through the resistance R5 also flows through the resistance R6 and the transistor Q2, thereby increasing the amount of the current (the flow 6 of current: B+ ---> R7 --> Q5 -+ L2 -+ Q4 -+ R6 -+ Q2).

If the earth magnetic field correction mode is set by 'Mode3', the orientation of the TV set is identified as the 'C' direction, so that the microprocessor 15 outputs the earth magnetic field correction signals S4 and S5 of high voltage. Then the transistors Q2 and Q8 are turned on, and thus, the transistors Q3 and Q6 are accordingly turned on, according to which a larger current flows in the 'B' direction (B+ --+ R7 -> Q3 -- L2 ---> Q6 -+ R6 -+ Q2), thereby correcting the degaussed state.

If the earth magnetic field correction mode is set by 'Mode4% the orientation of the TV set is identified as a 'D' direction, so that the microprocessor 15 outputs only the earth magnetic field correction signal S5 as a high voltage. Then, the transistor Q8 of the earth magnetic field correction unit 17 is turned on and the transistors Q3 and Q6 are accordingly turned on, so that a little current flows in the '13' direction (B+ -+ R7 -> Q3 -+ L2 -- > Q6 R5).

The state of the earth magnetic field correction unit 17 for the various outputs if the earth magnetic field correction signals S3-S5 according to setting of the earth magnetic field correction mode is shown in Figure 3.

That is, in this example of the conventional art, the earth magnetic field correction mode is selected depending on the orientation of the TV set, and according to which, when a corresponding mode is set, the earth magnetic field is automatically corrected, thereby providing images with distinct colors.

As another example of a conventional art shown in Figure 5, the Korean Laid Open No. 95-24598 discloses a deflection correction apparatus of a cathode ray tube which includes a correction value determining unit 110 having correction value signals corresponding to each direction and outputting each correction value signal; a direction sensing and selecting unit 120 for sensing 7 the orientation of the cathode ray tube and selectively outputting a correction value signal inputted from the correction amount determining unit 110 according to the sensing result; and a deflection correction unit 130 for correcting a deflection of the cathode ray tube according to the correction amount signal outputted from the direction sensing and selecting unit 120.

The direction sensing and selecting unit 120 includes a direction sensor for outputting a sensing result signal; and an output selecting switch for selectively outputting the correction amount signal of the correction amount determining unit I 10 according to the sensing result signal.

The operation of the deflection correction apparatus of a cathode ray tube according to the conventional art will now be described.

First, correction value signals according to each direction are stored in the correction amount determining unit I 10 at the time when the monitor is fabricated.

When an earth magnetic field correcting mode is set at the time when the monitor is placed, the orientation sensor of the sensing and selecting unit 120 sense the orientation of the cathode ray tube, and the output selecting switch selects a signal corresponding to the correction amount sig als outputted from M gn the correction amount determinina unit 110 and then outputs it to the deflection correction unit 130. Then, the deflection correction unit 130 corrects the deflection of the cathode ray tube corres onding to the correction amount signal p from the direction sensing and selecting unit 120, thereby providing an improved distinct color image.

However, because the orientation of the monitor is to be first identified by the compass and then the earth magnetic field correction mode is selected corresponding to the orientation identified, a lot of correction mode date need to be stored for correcting the earth magnetic field precisely. Thus, it requires a

8 large memory which increases the unit cost of production.

Also, since the earth magnetic field varies around the world, the problem of correcting the earth magnetic field for each area remains.

The present invention is defined in the accompanying independent claims. Some preferred features are recited in the dependent claims.

An object of the present invention is to provide an apparatus for automatically correcting an earth magnetic field for a monitor in which a screen is automatically corrected by sensing a peripheral magnetic field with only a small memory requirement, to provide convenience in correcting an earth magnetic field and maintain optimum picture quality.

To achieve these and other advantages and in accordance with the present invention, there is provided an apparatus for automatically correcting an earth magnetic field for a monitor including: peripheral magnetic field sensing means for sensing a variation of a magnetic field and generating a corresponding frequency; frequency producing means for arithmetically operating the frequency generated from the peripheral magnetic field sensing means and producing frequencies of each direction; correction amount computing, means for computing each correction amount corresponding to each frequency of each direction produced by the frequency producing means and deflection correction means for correctinc, a deflection error of the monitor as much as the corrected amount in the correction amount computing means.

The correction amount computing means converts the frequency of the frequency producing means to a magnetic field value according to a prestored frequency-magnetic correlative equation, and compares it with a pre-set reference magnetic field value to thereby compute a correction amount corresponding to a difference thereof.

The correction amount computing means may include a microprocessor 9 having a programmable 'memory in which a frequency-magn etic field correlative equation and a magnetic field-screen change correlative equation are stored to correct a tilt, a vertical position, a horizontal position and a purity landing (focus), and storing means (EEPROM) for storing initial screen data and a reference magnetic field value of each direction.

There is also provided a method for automatically correcting an earth magnetic field for a monitor including the steps of. setting reference magnetic field values corresponding to three axes of X, Y and Z; measuring a magnetic field of the directions of the three axes; discriminating whether or not the reference magnetic field value in the reference magnetic field value setting step and the measured magnetic field in the magnetic field measuring step are identical to each other; maintaining a tilt, a vertical position, a horizontal position and purity if the reference magnetic field value and the measured magnetic field in the discriminating step are correspond; and determining a correction amount by using a predetermined equation and correcting a tilt, a vertical position, a horizontal position and purity if the reference magnetic field value and the measured magnetic field value in the discriminating step do not correspond.

The present invention can be put into practice in various ways some of which will now be described by way of example with reference to the accompanying drawings in which:

Figure I is a circuit diagram of an apparatus for correcting an earth magnetic field in accordance one example of the prior art;

Figure 2 is exemplary views of on-screen displays in correcting an earth magnetic field according to the circuit of Figure 1;

Figure 3 shows a table for correcting the earth magnetic field according to the circuit of Figure 1; Figure 4 is a flow chart of an operation for correcting the magnetic field in accordance with the circuit of Figure 1;

Figure 5 is a schematic block diagram of a deflection correction apparatus of a cathode ray tube in accordance with another example of the prior art; Figure 6 is an exemplary view of coordinates for defining orientation; Figure 7 is a schematic block diagram of apparatus for automatically correcting an earth magnetic field for a monitor in accordance with the present invention;

Figure 8 shows a schematic block diagram of a frequency producing part of Figure 7 in accordance with the present invention; Figure 9 is an illustration of an operation of the frequency producing part of Figure 7 in accordance with the present invention; Figure 10 is an exemplary illustration of a conversion from a frequency to a magnetic field of Figure 7 in accordance with the present invention; and

Figures I I a, I I b and I I c are flow charts of operations for sensing a variation in a magnetic field and its correction in accordance with the present invention.

Figure 7 is a schematic block diagram of an apparatus for automatically correcting an earth magnetic field for a monitor which includes a peripheral magnetic field sensing, unit 210 for combining a magnetic field sensor and a resistance in a magneto-inductive mode both to apply a forward direction current and a reverse direction current, and generating a frequency according to a variation in the magnetic field existing at that time for each of the three mutually orthogonal axes X. Y and Z. A frequency producing unit 220 operates arithmetically to generate differences (Xjor - X-rev, Y-for - Y-rev Z-for - Z_rev) between a forward direction frequency ()Jor, Y-for and Z-for) for 11 each axis and a corresponding reverse direction frequency ()_rev, Y-rev and Z-rev) and to produce frequencies (fx, fy and fz) for each axis. A microprocessor 230 converts the frequencies (fx, fy and fz) of each axis of the frequency producing unit 220 into magnetic field values (Gx, Gy and Gz) of each axis when an on-screen display key 260 is actuated to set an earth magnetic field correction mode for comparing the magnetic field values (Gx,

Gy and Gz) of each axis with reference magnetic field values (G_Xref, G_Yref and G-Zref) to compute a correction amount corresponding to the difference.

A deflection correction unit 240 is used to correct a deflection of a monitor (250) by the correction amount from the microprocessor 230. A storing unit 270 pre-stores reference magnetic field values (G_Xref, G_Yref and G-Zref) for computing the correction amount, and initial screen data (i.e., tilt, Vpos, Hpos and purity, etc.) of a screen pre-set at the time when the monitor is fabricated, so as to be available to the microprocessor 230.

Figure 8 shows the components of the frequency producing unit of Figure 7 in accordance with the present invention. It includes a counter 300 for sequentially counting the forward direction frequency and the reverse direction frequency for each axis; a register 3 10 for temporarily storing the value counted at the counter; and an operating unit 320 for computing the difference between each forward direction frequency and its corresponding reverse direction frequency and producing frequencies for each axis based on the difference.

The magnetic field sensor of the peripheral ma Z:' gnetic field sensing unit

2 10 is installed parallel to each axis of the magnetic field.

The microprocessor 230 includes a pro( grammable memony storing a frequency-magrietic field correlative equation (EQ I x, EQ 1 y and EQ I z) and a magnetic field-screen variation correlative equation.

The storing unit 270 includes an EEPROM.

12 The operation of the apparatus for automatically correcting the earth magnetic field of a monitor constructed as described above will now be explained.

A magnetic field in space can be represented by a three-dimensional vector having the three axes Y, Y and Z. As shown in Figure 6, in the present invention, the magnetic field of each axis of orientation of the screen (X, Y and

Z) of the monitor is defined as X-axis direction magnetic field Gx, Yaxis direction magnetic field Gy and Z-axis direction magnetic field Gz.

First, the peripheral magnetic field sensing unit 210 is oscillated by combining a resistance and a sensor in a magneto-inductive mode so that the inductance is varied according to variation in the peripheral magnetic field.

In order to prevent any malfunction possibly caused by drift according to (e.g.) temperature change, the for-ward direction current and the reverse direction current flow in turn to the sensor in each axis in order to resonate the peripheral magnetic field sensing unit 210, so that the forward direction frequencies ()_fbr, Y-for and Z_for) and the reverse direction frequencies (N_rev, Y-rev and Z-rev) are generated.

Accordingly, the frequency producing unit 220 counts the forward direction frequencies QJor, Y-for and Z_for) and the reverse direction frequencies ()_rev, Y-rev and Z-rev) generated at the peripheral magnetic field sensing unit 2 10, stores them to its internal register, computes the difference (N_for-X-rev, Y-for-Y-rev and Z-for-Z rev) between the forward direction frequencies and the reverse direction frequencies, produces the final frequency for each axis (fx, fy and fz) by using the difference, and transfers them to the microprocessor 230.

The frequency producing unit 220 produces the frequencies (fx, fy and fz) for each axis according to the process of Figure 9 and includes, as shown in 13 Figure 8, a counter 300 for sequentially counting the forward direction frequencies QJor, Y-for and Zjor) and the reverse direction frequencies Qjev, Y-rev and Z_rev) of each axis (X, Y and Z). A re gister 3 10 stores the forward direction frequencies QJor, Y-7for and Z_for) and the reverse direction frequencies ()_rev, Y-rev and Z-rev) as counted and an operating unit 320 computes the difference QJbr-X_rev, Y-for-Y-rev and Z-for-Z-rev) between the forward direction frequencies and the reverse direction frequencies and produces the frequencies (fx, fy and fz) of each axis from the difference.

When the earth magnetic field correction mode is set by pressing the on screen display key 260, as shown in Figure 10, the microprocessor 230 converts the frequencies (fx, fy and fz) of each axis transferred from the frequency producing unit 220 into magnetic fields (Gx, Gy and Gz) according to the frequency (f)-magnetic field(G) correlative equation (EQ I x. EQ I y and EQ I z).

The frequency (f)-magnetic field(G) correlative equations (EQlx, EQly and EQlz) are those pre-set in the microprocessor 230. Each is obtained as follows: taking as an example, the X axis-magnetic field correlative equation (EQlx), if the monitor is arranged in the X-axis direction to give a magnetic field reading of "0.5G', its output frequency is measured and an output frequency at '-0.5G' is obtained. Then a straight line between the frequency (f) and the magnetic field (Gx) can be formed by using the obtained two output frequency values, by which a first equation of the straight line can be obtained.

The frequency-magnetic field correlative equation (EQlx, EQly and

EQ I z) can be expressed as follows:

EQlx = AN - B, EQly = Cfy + D, EQlz = Efz + F. where EQlx, EQly and EQlz respectively indicate magnetic fields (Gx, Gy and Gz) (Gauss) in the

X, Y and Z direction.

At this time, as shown in Figure 10, the microprocessor 230 keeps 14 comparing whether the reference magnetic field (G Xref

G_Yref and G-Zref), as pre-set in the EEPROM in the fabricating stage of the monitor, and the currently sensed magnetic fields (Gx, Gy and Gz) are identical so as to judge whether or not the screen state is to be corrected.

If the reference magnetic fields and the currently sensed magnetic field are identical, the microprocessor 230 operates the deflection correction unit 240 to maintain the current screen state of the monitor 250.

On the other hand, if the reference magnetic fields are not identical to the currently sensed magnetic fields, the microprocessor 230 recognises the axis direction in which the magnetic field differs so as to determine a correction amount according to a magnetic field-screen change correlative equation (EQ2_Tilt, EQ2_Vpos and EQ2-Hpos) pre-set for the corresponding axis.

The pre-set magnetic field-screen change correlative equation for each axis direction is obtained by a first equation over a screen direction change for a magnetic field. For example, in case of the tilt, the following equation is obtained.

EQ2-Tilt = AGx + B. where EQ2_Tilt is a tilt correction amount [mm], Gx is an X axis magnetic field [Gauss].

For correction of the tilt. when a correction amount is determined by the magnetic field-screen change correlative equation, the microprocessor 230 adjusts a duty width of a PV;Nl pulse for adjusting the tilt by the correction amount and transfers it to the deflection correction unit 240, so that the current of a tilt coil is changed, and the tilt is corrected accordingly.

Likewise, the magnetic field-screen change correlative equation (EQ2

Vpos and EQ2-Hpos) for correcting the vertical position and the horizontal position can be obtained by the following equations:

EQ2-Vpos = CGy + D, EQ2_Hpos = EGz + F. EQ2_Vpos is a vertical position correction amount, EQ2_Hpos is a horizontal position correction amount.

Accordingly, in case of the correction of the vertical position or the horizontal position, like the tilt correction process, the microprocessor 230 computes the correction amount, adjusts the duty width of the PWM pulse for adjusting the vertical position or the horizontal position as much as the correction amount, and transfers it to the deflection correction unit 240, so that the current of a vertical position coil or a horizontal position coil is changed, and accordingly the vertical position or the horizontal position are corrected.

After the correction amount of the horizontal position, vertical position and the tilt are found as stated above, a purity correction is performed by controlling a beam landing at four comers of the screen of the monitor 250.

Figures Ila, Ilb and Ilc are flow charts of operations for sensing a variation in a magnetic field and its correction in accordance with the present invention.

Figure Ila is a flow chart of an operation for sensing and correcting a magnetic field variation in the X axis. First, a Tilt reference magnetic field value (G_Xref) of X direction is set in step S 1. and a magnetic field (Gx) of the

X direction is set in step S2. Then, it is judged whether or not the tilt reference magnetic field value (G_Xref)'is identical to the magnetic field value (Gx) if the

X direction, and, if the two are identical, the tilt and the purity is maintained in step S4, while if the two are not identical, a correctionamount is determined by the equation EQ2-tilt in step S5, thereby correcting the tilt and the purity in step S6.

Figure I I b is a flow chart of an operation for sensing and correcting a magnetic field variation in the axis. First, a vertical position reference magnetic field value (G_Yref) in the Y direction is set in step SI, and a magnetic field

16 (Gy) of the Y axis is measured in step S2. Then, it is judged whether or not the vertical position reference magnetic field value (G_Yref) is identical to the magnetic field value (Gy) and, if the two are identical, the Vpos and the purity are maintained in step S4. If the two are not identical, a correction amount is determined by the equation of EQ2_Vpos in step S5, thereby correcting the Vpos and the purity in step S6. Figure I I c is a flow chart of an operation for sensing and correcting a magnetic field variation in the Z axis. First, a horizontal position reference magnetic field value (G_Zref) of Z direction is set in step S1, and a magnetic field (Gz) in the Z direction is measured in step S2. Tben, its is judged whether or not the vertical position reference magnetic field value (G_Zref) is identical to the magnetic field value (Gz) in the Z axis in step S3, and if the two are identical, the Hpos and the purity are maintained in a step S4. If the two are not identical, a correction amount is determined by the equation of EQ2_Hpos, thereby correcting the Hpos and the purity.

As so far described, according to the apparatus for automatically correcting the earth magnetic field of the monitor, when the earth magnetic field correction mode is set, a peripheral magnetic field is detected and magnetic field correction amounts for each axis are automatically computed, so as to correct the magnetic field by the correction amount. thereby providing user convenience and improved product reliability. Also, since the size of the memory can be reduced, its unit cost of production can be reduced accordingly.

As the present invention may be embodied in several forms without departing from the essential characteristics thereof. it should also be understood M 1 that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly according to the scope of the appended claims. All changes 17 and modifications that fall within the scope of the claims, or equivalents thereof are therefore intended to be embraced by the appended claims.

18

Claims

CLAIMS:

1. An apparatus for automatically correcting for earth magnetic field effects on a monitor, the apparatus comprising:

peripheral magnetic field sensing means for sensing a magnetic field with respect to at least one datum of orientation; frequency producing means for producing a frequency corresponding to the magnetic field in each direction from an output of the peripheral magnetic field sensin means 9 V correction value computing means for computing a correction value corresponding to the said frequencies produced by the frequency producing means; and deflection correction means for correcting a deflection offset of the monitor by the correction value from the correction value computing means.

2. The apparatus according to claim 1, wherein the frequency producing means includes:

a counter for sequentially counting a forward direction frequency and a reverse direction frequency associated with the magnetic field; a register for temporarily storing, the value at the counter; and operating means for computing the difference between the forward direction frequency and the reverse direction frequency and producing a difference frequency. the correction value computing means being"operable to compute the correction value based upon the said difference frequency.

3. Apparatus according to claim 1. wherein the correction value computing means includes:

19 a microprocessor for converting frequencies of each direction produced by the frequency producing means into a magnetic field value of each direction, comparing the magnetic field value of each direction with a reference magnetic field value and computing the correction value corresponding to a difference between them; and storing means for pre-storing the reference magnetic field value for the computation of the correction value and providing it to the microprocessor.

4. The apparatus according to claim I or 3, wherein the correction value computing means computes a beam incidence correction amount on the basis of a magnetic field variation of a horizontal position or a vertical position.

5. The apparatus according to any of claims I to 4, wherein the peripheral magnetic field sensing means are arranged to sense the magnetic field with respect to a plurality of predetermined axes, the frequency producing means being operable to produce a frequency corresponding to the magnetic field in each direction with respect to each axis, the correction value computing means being operable to compute a correction value for each axis and the deflection correction means being operable to correct the deflection offset according to each of the correction values.

6. The apparatus according to claim 5 in which the axes are arranged mutually orthogonal to one another.

7. A method for automaticall-%- correcting an earth magnetic field for a monitor comprising the steps of:

setting a reference magnetic field value corresponding to three axes of X.

Y and Z; measuring a magnetic field along the three axes; determining whether or not the reference magnetic field value and the measured magnetic field correspond; maintaining tilt, vertical position, horizontal position and purity, if the reference magnetic field value and the measured magnetic field correspond; and determining a correction amount by using a predetermined equation and correcting tilt, vertical position, horizontal position and/or purity, if the reference to magnetic field value and the measured magnetic field do not correspond.

8. The method according to claim 7, wherein the predetermined equation is AGx + B and/or CGy + D and/or EGz + F, wherein Gx is the magnetic field in the X-axis, Gy is the magnetic field in the Y-axis, Gz is the magnetic field in the Z-axis.